This application claims the priority of Korean Patent Application No. 2002-25909, filed May 10, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a high-density data storage apparatus using a scanning probe microscopy (SPM) technique, a data recording method, and a data reproducing method, and more particularly, to a data storage apparatus capable of rapidly recording and reproducing data with a high density using a capacitance detector, and a data recording method and a data reproducing method both using the data storage apparatus.
2. Description of the Related Art
A high-speed, high-density data storage apparatus using an SPM technique is composed of a cantilever array of cantilevers each having a tip to record or reproduce data, a recording medium for storing data, a stage for driving the recording medium in the directions of X and Y axes, and a controller.
Data is reproduced from the recording medium by detecting a change in the properties of cantilevers, which is generated due to the interaction between the recording medium and the tips. As the speed of data reproduction is restricted by the frequency characteristics of a cantilever, the detection of a plurality of data using a single cantilever affects the speed of data reproduction. In order to reduce this problem, there has been proposed a method of recording data to and reproducing data from a recording medium using a plurality of cantilevers.
Type of data storage techniques using a probe includes a capacitance detection technique for detecting a change in the capacitance, and a scanning capacitance microscopy (SCM) technique for detecting a change in the resonance frequency or oscillating width using an oscillator.
A brief conceptual diagram of a conventional cantilever using the capacitance detection technique is shown in FIG. 1. Referring to FIG. 1A, a cantilever 2, whose one end is fixed to a fixed end, is connected to an electrode 3 to form a capacitor with the electrode 3. A tip 4 is attached to the other end of the cantilever 2, which is free. While the cantilever 2 moves over the surface of the recording medium, the end of the cantilever 2 that has the tip 4 moves in the direction perpendicular to the surface of the recording medium, that is, in the Z-axis direction, due to the interaction between the tip 4 and the surface of the recording medium. At this time, the capacitance of the capacitor formed by the cantilever 2 and the electrode 3 changes.
An equivalent circuit of the conventional cantilever adopting the capacitance detection technique of FIG. 1A is shown in FIG. 1B. In such a conventional data storage apparatus adopting the capacitance detection technique, the detected current induced by the capacitance change is proportional to the sum of a nominal capacitance value and a variation in the capacitance. This makes it difficult to improve the amplification and sensitivity of a signal.
FIGS. 2A and 2B are a conceptual diagram and its equivalent circuit, respectively, of a conventional differential cantilever configured such as to compensate for the defects of the capacitance detection technique adopted by the cantilever device shown in FIGS. 1A and 1B in order to detect only the variation in capacitance.
Referring to FIG. 2A, the center of a conventional differential cantilever 8 with a tip 11 is supported by a supporter 12, a cantilever portion on the left side of the supporter 12 forms a capacitor together with an electrode 9, and a cantilever portion on the right side of the supporter 12 forms a capacitor together with an electrode 10. As the conventional differential cantilever 8 is supported at its center by the supporter 12, it records and reproduces data while one end having the tip 11 descends by lifting the other end.
The differential cantilever 8 is better than the existing cantilever 2 in terms of the linearity and the size and sensitivity of a detection signal. However, the differential cantilever 8 requires a great amount of driving force because the driving displacement increases due to the increased width of the supporter 12 and the length of the cantilever 8 twice as long as the existing cantilever 2. In order to overcome the drawback, a conventional data storage apparatus adopts an array of the plurality of cantilevers 8 and records and reproduces data by moving a recording medium in directions X and Y.
FIGS. 3A and 3B illustrate a method of recording and reproducing data using a plurality of conventional cantilevers to each of which a sensor is connected. Referring to FIG. 3A, sensors S1, S2, S3 and S4 are connected to cantilevers 11, 13, 15 and 17, respectively, to individually apply a data recording signal to the cantilevers and individually detect a data reproduction signal from them.
As shown in FIG. 3B, each of the sensors detects one data detection signal for each data area. In such a case where a plurality of cantilevers are controlled by a plurality of sensors, the recording and reproduction speeds are improved in proportion to the number of cantilevers. On the other hand, a detection and recording circuit for the cantilevers occupies a large area, and power consumption increases.